This study concerns the effects of marijuana smoking on actual driving performance. It presents the major results of one laboratory and three on-road driving studies. The latter were conducted on a closed section of a primary highway, on a highway in the presence of other traffic and in urban traffic, respectively. This program of research has shown that marijuana produces a moderate degree of driving impairment which is related to the consumed delta9-tetrahydrocannabinol (THC) dose. The impairment manifests itself mainly in the ability to maintain a steady lateral position on the road, but its magnitude is not exceptional in comparison with changes produced by many medicinal drugs and alcohol. Drivers under the influence of marijuana retain insight in their performance and will compensate where they can. As a consequence, THC's adverse effects on driving performance appeared relatively small in the tests employed in this program. (A)
Abstract